The present invention relates to a mold die for manufacturing an optical module for integrally holding component parts such as optical connectors, optical operation elements, and electronic circuit parts by a molding resin, and manufacturing method using the mold die.
In manufacturing an optical module by transfer molding using a molding resin, the longitudinal accuracy, positional accuracy, and angular accuracy of an optical connector relative to its package are important. Furthermore, in manufacturing a multicore optical module having a plurality of optical connectors, it is necessary to ensure sufficient positional accuracy (pitch and parallelism) among the optical connectors. Conventionally, the optical module is manufactured as following process.
First, electronic circuit parts such as bare chips are mounted on a substrate on which a wiring pattern formed by die bonding or the like. Furthermore, the electronic circuit constituted by the electronic circuit parts mounted on the substrate is connected to an inner lead or an optical operation element, such as a light-emitting element or a light-receiving element, fixed to a connector. An assembly thus formed is then placed in a transfer mold, and is subjected to resin molding so as to be formed as a unit. Subsequently, unnecessary portions of a lead frame are removed and lead pins are bent, hence completing an optical module.
FIGS. 17 and 18 are perspective views illustrating a transfer mold die used for manufacturing a conventional multicore optical module. This mold die comprises an upper die 1 (FIG. 18) and a lower die 2 (FIG. 17), and two cavities 1a, 2a are formed on mutually opposing surfaces of the upper die 1 and the lower die 2. A pair of semicylindrical concave portions 1b, 2b are formed in communication with the respective cavities 1a, 2a. The component parts such as the lead frame are placed between the upper die 1 and the lower die 2 and, in this case, one end side of the optical connector for receiving an end of an optical fiber is adapted to be fitted closely into the concave portions 1b, 2b. As a pair of optical connectors are fitted in these concave portions 1b, 2b, the relative positional relationship between the optical connectors is determined.
FIG. 19 is a cross-sectional view illustrating a state in which the optical module formed by transfer molding described above is connected to an optical plug via a receptacle. Here, an optical module 40 is inserted into one end portion of a receptacle 41, while an optical plug 42 having a ferrule 43 is inserted into the other end portion of the receptacle 41. Thus, an optical coupling is established between the optical fiber held by the ferrule 43 and an optical operation element fixed to an optical connector 34. At this juncture, as the optical module 40 is secured by the one end portion of the receptacle 41, the position of the optical connector 34 in the longitudinal direction and in a direction perpendicular thereto is determined at the one end portion of the receptacle 41. Meanwhile, as for the optical plug 42, the position of the ferrule 43 in the longitudinal direction and in a direction perpendicular thereto is determined at the other end portion. Accordingly, in order to position the optical connector 34 and the ferrule 43 with in the receptacle 41 with high accuracy, it is necessary to ensure the positional accuracy and angular accuracy of the optical connector 34 with respect to the outer peripheral dimensions of a package portion of the optical module 40. Unless these accuracies are ensured, the ferrule 43 partially abuts against the optical connector at the time of attachment and detachment of the optical plug, so that the abrasion, breakage, and the like of the ferrule and the interior of the optical connector occur.
In addition, if the pin length (the length of the optical connector projecting from a resin portion) of the resin-molded optical connector 34 is inaccurate, it becomes impossible to effect an adequate optical coupling, or in a case where the pin length has become extremely short, a stress is applied to a wire connecting the optical connector and the circuit, which is therefore undesirable. For this reason, it is necessary to accurately position the optical connector at the time of resin molding.
According to a conventional method of manufacturing an optical module, stopper surfaces 1s, 2s are provided for the concave portions 1b, 2b of the mold die in which the optical connector is secured, with respect to the direction in which the optical connector moves away from the cavities 1a, 2a in the longitudinal direction (in the axial direction of the optical connector) of the concave portions 1b, 2b. However, no restrictions have been provided with respect to the direction in which the optical connector approaches the cavities 1a, 2a. For that reason, if the optical connector moves due to vibrations or the like at the time of aligning the upper die 1 to the lower die 2 of the mold die, there is the possibility that the optical module is formed in a state in which the optical connector is located closer to the cavities 1a, 2a from its predetermined position, thereby shortening the pin length of the optical connector projecting from the molding resin member.
In addition, the optical modules have hitherto been manufactured by using a mold die having semicircular alignment channels, and the semicircular alignment channels have been formed by drilling. Therefore, there have been drawbacks in that it is difficult to control the machining depth of the alignment channels and prevent the inclination of the axis owing to variations in the run-out of the drill between the top portion and the proximal portion of the drill during rotation, and that sagging is liable to occur to an edge of a machining portion. Hence, there have been limitations to the ensuring of the positional accuracy and angular accuracy of the optical connector.